Two stroke cycle internal combustion engines



Dec. 1, 1964 A. E. BROWN TWO STROKE CYCLE INTERNAL COMBUSTION ENGINES Filed July 15, 1962 4 Sheets-Sheet 1 1 FIG. I

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4 Sheets-Sheet 2 A. E. BROWN TWO STROKE CYCLE INTERNAL CQMBUSTION ENGINES Dec. 1, 1964 Filed July 13, 1962 Mil/Lam A. E. BROWN 3,159,147

TWO STROKE CYCLE INTERNAL CQMBUSTION ENGINES 4 Sheets-Sheet I5 7 FIG. I:

Quad Lam & 2 8 W ,7. I 5 m l \\\\\k\\- I H\\\\\\\ w mm m w I I 7 6 Dec. 1, 1964 Filed July 13, 1962 United States Patent 3,15%147 TWG STROKE CYCLE INTERNAL COMTEUSTION ENGINES Arthur E. Brown, Nahaut, Mass. (118 W. 6th St., Corning, NY.) Fiied July 13, 1962, Ser. No. 269,619 18 Claims. (Cl. 123-41316) This invention relates to two stroke cycle internal combustion engines and more particularly to the double acting type.

In a two stroke cycle engine, it is often customary to employ two or more cylinders instead of a single large cylinder in order to obtain an engine of given displacement and power output because this gives a smoother flow of power with two or more smaller impulses per revolution instead of a single large impulse. An advantage of this invention is that the engine is two stroke cycle double acting and therefore has two power strokes per revolution of each crank. The single crank engine shown in FIG. I can therefore take the place of a two cylinder single acting two stroke cycle engine or a four cylinder single acting four stroke cycle engine.

A general object of the invention is to provide an engine that is light in weight and compact in overall size for a given power output.

Another object is to provide a double acting two stroke cycle internal combustion engine which is self scavenged and is without the need of a separate scavenge pump or blower.

Another object of the invention is to improve the thermal efliciency by employing uniflow scavenging in place of cross flow or loop scavenging. The flow of scavenging air (or fuel air mixture) through each working chamber is orderly in character with less mixing, less short circuiting, and less eddy currents than are associated with cross how or loop scavenging. In conventional carbureted cross scavenge and loop scavenge engines, a portion of the inlet flow is short circuited to the exhaust port so that unburned carbureted fuel is lost out the exhaust port. This is the principal reason why cross scavenged carburetor engines show a poor thermal eificiency compared with four stroke cycle engines.

An advantage of the engine is that it is able to operate at high speed without subjecting the connecting rod, crankshaft, and bearings to high reciprocating inertia forces. The double acting piston assembly is cushioned at the end of each stroke by a gas pressure force which opposes the reciprocating inertia force.

A common problem in a single acting two stroke cycle engine is failure of the wrist pin or piston pin bearing. This is because the load on that bearing is unidirectional and there is diificulty in getting an oil film under the highly loaded oscillating bearing. In a double acting engine, as described in this invention, the load on the wrist pin bearing is bi-directional instead of unidirectional. This load reversal permits the bearing to belubricated by the so called squeeze film action. I e

The engine is well suited to operate at high speed be cause of its inherent free breathing.characteristics made. possible by uniflow. scavenging andflarge port areas. The port areas are large, yet the port heights are minimized so as to retain a long effective power stroke. The desirable combination of large port areas but minimum port height is made possible because the exhaust ports are distributed around the full periphery of the cylinder in stead of just a portion of the periphery (as in cross scavenged engines).

Another object of the invention is to simplify the construction of the engine by employing a single long structural cylinder with a common cylinder head or partition combustion pressure on piston 11. The rod as shown is cast into the aluminum piston It The connecting rod inserted midway in the cylinder and held in place by dowel pins or other means.

An advantageous feature of this invention is that the pistons remain cooler since each worlnng piston is exposed to combustion on one side only. Also, the flow of scavenging air through the pistons aids the cooling process. a In one embodiment of this invention (FIG. II) an object is to turbocharge the engine and provide simple means for starting the engine without the need of a gear train for driving the turbocharger.

The engine is light in weight and compact in overall size because: (1) is is double acting; (2) It is well suited to operate at high speed; and (3) It has a higher mean efiective pressure because of uniflow scavenging and short port height.

These and other objects and advantages will be made more apparent from the following description:

FIGURE I is a sectional view of one form of the invention in which the engine is self scavenged and in which a hollow piston rod is sealed with contracting type rings.

FIGURE II is a view of another embodiment of the invention in which the engine is turbocharged and in which a hollow piston rod is sealed with contracting type rings. The main engine parts in FIG. II are shown as a section View whereas the turbocharger is shown diagrarnatically without showing its details of construction. The engine shown in FIG. II is suited for a higher power range than the engine shown in FIG. I.

FIGURE III is a sectional View of another form of the invention in which the engine is self scavenged and in which valve pistons are attached to the working pistons.

FIGURE IV is a sectional view of another form of the invention in which the engine is supplied with scavenge air from a Roots type blower (shown diagrammatically) and in which valve pistons are attached to the working pistons. The engine shown in FIG. IV is suited for a higher power range than the engine shown in FIG. III.

In the following description and claims, the words front and bac refer to location of the parts so prefixed. Front means closer to the crankshaft and back means farther from the crankshaft, i.e., the front cylinder is closer to the crankshaft than the back cylinder.

liner 4 and held in place with removable tapered dowel pins 6. The head is sealed in the liner by means of the ring 7. If desired, the cylinder head may be fitted into the liner 4 with a shrink fit so that the ring 7 would not be required. The cylinder head 5 thus separates or divides the long cylinder structure 3 into two working cylinders which are termed a front working cylinder 8 and a back Working cylinder 9. A front working piston 10 and a back working piston 11 are located in their respective cylinders: r The cylinder head 5 is provided with a bore through which passes the hollow reciprocable rod 12. The two working pistons 10 and 11 reciprocate together as an assembly since they are joined together by means of the hollow rod 12. The rod 12 should be hard enough to resist wear from the contracting type seal rings 13 and should be strong enough to withstand the force due to 14 connects the piston pin 15 to the crankshaft. The central bore in the head 5 is provided with contracting rings 13 which seal against the rod 12. The rod'is provided with inlet ports 16 and 17 passing through the wall of the hollow rod. A partition 18 within the rod prevents through passage of air during alternate pumping strokes. Numbers 19 indicate passages for coolant.

Operation of the engine shown in FIG. I is as follows: On piston upstroke, a fuel-air mixture from a carburetor (not shown) is drawn through pressure actuated reed valve 26 into the crankcase. On downstro-ke, the mixtom dead center, the piston 14%} first uncovers the front exhaust ports 21 so as to provide a short exhaust blow down period. Then the front inlet ports 16 are brought in open communication with the front power chamber 22. The mixture in the crankcase flows through the hollow rod 12, through front inlet ports 16, and into the front power chamber 22 which is then scavenged with a uniiiow type scavenging action exhausting at ports 2 1. 011 upstroke the mixture in chamber 22 is compressed, then fired either by carburation, fuel gas-air mixing valve, or fuel injection. On downstroke the air or air-fuel mixture in chamber 46 is compressed, then fired by ignition plug 41.

Exhaust gas from ports 38 is conducted to the turbine inlet nozzles of the turbocharger 42 so that the turbine wheel 43 drives centrifugal compressor wheel 44., Since the outlet 45 of the centrifugal compressor is blocked by the butterfly valve 34 during starting, the turbocharger ture is partially compressed in the crankcase. Near botby ignition plug 23. The scavenging action is said to be first uncovers'the back exhaust ports 26 and then the back inlet ports 17 are brought in open communication with the back power chamber 27 which is then scavenged with a uniflow type scavenging action exhausting at ports 26. On downstroke the mixture in chamber 27 is compressed,

If desired, the two working cylinders 8 and 9 may be fabricated individually and joined to the cylinder head 5 by means of a bolted flange connection. However, with then fired by an ignition plug (not seen in the section V view shown).

the construction shown, the cylinders 8 and 9 can be formed in one operation with no need for flanges or boling. The single cylinder liner 4 can be turned, bored, and ground in single operations so that it is not necessary to set up, turn, and grind two separate liners. Also, with the construction shown in FIG. 1, two or more double acting cylinders can be closely spaced in parallel formation in a common cylinder block (in the sarne'manner as single acting engines) since there is no bolted flange mounting to interfere with the cylinder spacing. 7 C011- centricity and alignment is assured by making the cylinders 8 and 9 integral with a single long cylinder liner 4 bored in one operation.

If desired, fuel may be supplied to the FIG. I engine buration of the inlet'air.

7 Referring to FIG. II, the general construction of the engine is similar to FIG. I. The front end of the hollow rod 36 is formed with a tang 31. The piston pin 32 passes "through a hole in the tang with a press fit. The connecting rod 33 is forked at its-small end so as to straddle the tang.

Operation of the engine shown in F1611 is as follows: For starting and low speed operation, the butterfly valve 34 is moved to and held inthe closed position. On downstroke, air is drawn through pressure actuated reed valves 35 into the chamber 37. On upstroke, the back working piston 36 partially compresses the air in chamber 37.]

Near top dead center, the piston 36 first partly uncovers by injection into the power chambers instead of by car- ,7

the back exhaust ports 38 m as to provide an exhaust blow down period. Then the inlet ports 39am brought in open communication with the back powerchamber 4t 70 The partially compressedair in chamber 37 then flows through the hollow rod or tube 3tl,'through inlet ports 39 and into the back power chamber all which 'is. then scavenged with auniflow type scavenging action exhausting at ports 38; Fuel may be added by means not shown valve 34 is opened and the turbocharger then supplies scavenge air to both the back power chamber 40 and the front power chamber 46, through the common inlet ports 39. Both power chambers are scavenged with a uniflow type'scavenging operation exhausting at ports 38 and 47.

It is thus seen that the engine in FIG. 11 operates single acting during starting (using chamber 46 and reed valves 35 as a scavenge pump) and double acting after the turbocharger builds up a sufficient speed and output pressure. An advantage of this arrangement is that it is not necessary to provide a gear train for driving the turbocharger during starting. Also, it is not necessary to provide a source of stored compressed air for driving the turbocharger during starting.

The turbinemanifold 43 is divided with a partition 49 so that half of the nozzles 50 are fed from duct 51 and the other nozzles 52 are fed from duct 53 thus giving more exhaust pulse energy to the turbine;

Referring to FIG. III, a long structural cylinder 55 is fitted with a single liner 56. A common cylinder head or partition 57 is inserted into the liner and held in place with tapered dowel pins 58 and sealed with 0 provided-with seal rings and so is the back valve piston 65. A reciprocable rod 66 passes through the bore in the cylinder head and is attached to both of the working pistons. The rod is forked at its front end so as to straddle the small end 'of the connecting rod 67 and attach directly to the piston pin 68 In this manner, the tension force in the rod 66 (due to combustion pressure on the back working piston 63) is transferred directly to the connecting rod 67 through the piston pin 68. The back end of the rod 66 is fastened to the back working piston 63 by means of a perforated cone structure 69. The rod 66 is loaded in tension during running, with minor compression loads occurring during starting of the engine. When at top dead center, the inertia force of the back working piston 63 causes a tension load in the rod 66.

W'hen at bottom dead center, the combustion pressure rod 66 is loaded in tension for the most part means that the rodcan be small in diameter and light in weight since it issubject to only small compression loads as a column.

' .The circular disk 76 (which is attached tothe rod 66) conforms with a slidingfit to the herein. the cylinder head and is provided with aseal ring at its periphery. The

purpose" of the disk is to serve as a sliding seal separating the two pumping chambers andthereby prevent the alternate flow of air from onezpumping'chamberto the other as each working piston alternately pumps air for scavenging. The front inlet ports 71 and back inlet ports 721are in'the form of slots milled or cast into the cylinder head 57.

Operation of the engine shown in FIG. IlI is as follows: On piston upstroke, a fuel-air; mixture (from a carburetor not shown) is drawn through the pressure responsive reed valve 73 into crankcase 74. On downstroke the mixture is partially compressed in the crankcase. Near bottom dead center, the front working pis ton 62 first uncovers the exhaust ports 75 and then the front valve piston 64 uncovers the front inlet ports 71. The partially compressed mixture in the crankcase then flows up through the hollow front valve piston 64, through the inlet ports 71, and into the front power chamber 76 which is then scavenged with a uniflow type scavenging operation exhausting at ports 75. On upstroke the mixture in chamber 76 is compressed, then fired by ignition plug 77.

Also, on downstroke, a fuel-air mixture is drawn through reed valve 78 into the back pump chamber 79. On upstroke, the mixture is partially compressed in chamber 79. Near top dead center, the back working piston 63 first uncovers the exhaust ports 80 and then the back valve piston 65 uncovers the back inlet ports 72. The mixture flows through the perforated cone, through the hollow back valve piston 65, and through the inlet ports 72 so as to scavenge the back power chamber 81 with a uniflow type scavenging operation exhausting at ports 80. On downstroke the mixture in chamber 81 is compressed, then fired by ignition plug 82.

Referring to FIG. IV, the engine shown is similar in construction to FIG. III'except that a separate scavenge blower 84 is provided and no reed valves or circular disk 70 are employed. The engine shown in FIG. IV is suited for a higher power range and for a more continuous duty than the engine shown in FIG. III. The crankcase compartment 85 is not used as an air pump for scavenging and therefore may be provided with a pumped oil lubrication system. If desired, the fuel may be injected into the power chambers directly (instead of being mixed with the inlet air). In this manner the loss of unburned fuel out the exhaust ports during scavenging may be reduced even further. 7

Operation of the engine shown in FIG. IV is as follows: The Roots type blower 84 supplies scavenging air through the hollow back valve piston 86 to the annular gap 87 located between the ends of the front and back valve pistons 88 and 86. As the valve pistons reciprocate, the annular gap 87 is alternately brought into communication with the front inlet ports 89 and back inlet ports 90 so as to alternately supply scavenging air to the power chambers 91 and 92. Each power chamber'is scavenged with a unifiow type scavenging operation exhausting at ports 93 and 94 (controlled by the working pistons 95 and 96).

If desired, the inlet air and exhaust connections may be reversed in the FIG.- IV engine. That is the output flow from the blower 84 may be ducted to the ports 93 and 94 and the exhaust gas conducted out at 97.

While the preferred embodiments of the invention have been described, it will be understood that the invention is not limited thereto since it may be otherwise embodied within the scope of the following claims.

What is claimed is:

1. In a double acting two stroke cycle internal combustion engine, the combination of a crankcase, a crankshaft rotatably mounted in said crankcase, a front cyl-' inder mounted on said crankcase, a front piston re ciprocable in said front cylinder, a connecting rod for converting the reciprocating motion of said front piston to the rotary motion of said crankshaft, a back cylinder mounted behind said front cylinder, a back piston reciprocable in said back cylinder, a'cylinder headlocated 7 between said front cylinder and said back cylinder, said cylinder head having a cylindrical bore smaller in diameter than either of said cylinders, a reciprocable rod bore in the cylinder head and adapted to reciprocate therein, each tubular section being fitted with at least one expanding type seal ring, said tubular sections ending within said cylindrical bore, said tubular sections serving to conduct air, said reciprocable rod serving to transmit the force of combustion from said back piston to said connecting rod, a disk attached to said reciprocable rod and located between the ends of said tubular sections, said disk conforming at its outer diameter to said cylindrical bore in the cylinder head so as to form a sliding seal, and the purpose of said disk being to prevent loss of air pressure from theinterior of each tubular section into the other as each piston alternately pumps air for scavenging.

2. In a double acting two stroke cycle internal combustion engine, the combination of a crankcase, a crankshaft rotatably mounted in said crankcase, a front cylinder' connected to said crankcase, a front piston reciprocable in said front cylinder, a connecting rod for converting the reciprocating motion of said front piston to the rotary motion of said crankshaft, a back cylinder mounted behind said front cylinder, a back piston reciprocable in said back cylinder, a cylinder head located between said cylinders, said cylinder head having a cylindrical bore smaller in diameter than either of said cylinders, said two pistons being mechanically interconnected through said bore in the cylinder head so as to reciprocate in unison, each of said cylinders having exhaust ports located in the cylinder walls, each piston being adapted to control and uncover the exhaust ports in its respective cylinder, each said cylinder having within it a power chamber and a pump chamber. separated by its respective piston, the pump chamber in the front cylinder being in open communication with the interior of said crankcase, valve means for admitting air into the interior of each of said pump chambers and for preventing its escape, each of said pistons having a reduced diameter tubular section extending into said bore in the cylinder head and reciprocable therein, each of said tubular sections being provided with at least one ring groove and an expanding type seal ring adapted to seal within said cylindrical bore in the cylinder head, said cylinder head' having inlet ports interrupting its cylindrical bore near each end,-the purpose of said inlet ports being for passage of inlet air into each power chamber, each pump chamber with its respective piston serving as a scavenge pump for supplying air to its respective power chamber through its respective tubular section and through its respective inlet ports in the cylinder head, and each power chamber having a uniflow scavenging operation exhausting through said exhaust ports.

3. The combination recited in claim 2 wherein said two pistons are mechanically interconnected through said bore in the cylinder head by means of a reciprocable rod.

4. In a double acting two stroke cycle internal combustion engine, the combination of a structural cylinder adapted to be fabricated as a single structural cylinder, a cylinder head partition inserted inside said structural cylinder so as to divide the structural cylinder into two individual working engine cylinders, retaining means holding said cylinder head partition in position inside said structural cylnder, a working piston reciprocable in each of said working engine cylinders, said cylinder head partition having a cylindrical bore smaller in diameter than either of said working cylinders, each of said working pistons having a reduced diameter'tubular section extending into said cylindrical bore in the cylinder head partition and reciprocable therein, said two pistons being me-' i least'one ring groove and seal ring for sealing inside said cylindrical bore in the cylinder head partition, said cylinare covered and uncovered during the reciprocating motion of said tubular sections.

5. The combination recited in claim 4 wherein the said inserted cylinder head partition is provided vwith internal passages for the circulation of liquid coolanhand wherein the coolant enters andexits said inserted cylinder head partition via passages through the wall of said structural cylinder.

6. The combination recited in claim 4 wherein two spark plugs are fastened into the wall of said structural cylinder at locations which place the plugs points of ignition in direct communication with two of said inlet ports in the cylinder head.

7. in a double acting two stroke cycle internal combustion engine, the cornbinationof two cylinders mounted in tandem, a piston reciprocable in each cylinder, a cylinder head located between said cylinders, said cylinder head having a cylindrical bore smaller in diameter than either .of said cylinders, a reciprocable rod passing through said bore in the cylinder head and fastened to each of said pistons so as to reciprocate with the pistons, each of said pistons having a reduced diameter tubular section extend ing into said bore in the cylinder head and reciprocable therein, each of said tubular sections being provided with at least one ring groove and an expanding type seal ring for sealing inside said bore in the cylinder head, said reciprocable rod serving to transmit the force of combustion from one of said pistons to the other, said tubular sections serving to conduct air within them, a disk located between the ends of said tubular sections, saiddisk conforming at its outer diameter'to said cylindrical bore in the cylinder so as to form a sliding seal, the purpose of said disk being to prevent loss of air pressure from the interior of each tubular section into theother as each piston alternately pumps air for scavenging, and at least one of said tubular sections being separated from said disk by agap between the end of the tubular section and said disk.

8. The combination recited in claim 7 wherein said "disk is provided with a circumferential ring groove and an expanding type seal ring in said circumferential groove adapted to seal against the wall of said cylindrical bore in the cylinder head.

9. The combination recited in claim 7 wherein said cylinder head is provided near each end with inlet ports interrupting the cylindrical bore. in the cylinder head, and the purpose of said inlet ports being for the flow of scavenge air from said'cylindrical bore when each piston is near one endof its stroke.

10. In a double acting two stroke cycle internal combustion engine, the combination of a structural cylinder made of a single casting, a single cylinder liner inserted in said structural cylinder, a cylinderhead'partition inserted inside said cylinder liner so as to divide said structural cylinder with liner. into two individual working err-- gine cylinders, a working reciprocable piston inside each of said working engine cylinders, said cylinder head partition having a cylindrical bore smaller in diameter than either of said working engine cylinders, said two pistons beingmechanicaliyinterconnected through said bore in cylinder liner having openings through the shell of the liner for the entrance and'exit of the liquid coolant into it and out of said inserted cylinder head partitioineach of i said working engine cylinders having within it a power.-

. chamber adjacent said inserted cylinder head partition,

j at least one spark plug foreach .of said power chambers,v

said'cylinder liner having an opening in its shell for bringing each spark plug in firing communication with its respective power chamber, and means for supplying scavenge bustion engine, the combination of at least one structural cylinder, a cylinder head partition inserted inside said structural cylinder so as to divide said structural cylinder into two individual working engine cylinders, retaining means in the wall of said structural cylinder holding said cylinder head partition in position inside the structural cylinder, a working piston reciprocable in each of said working engine cylinders, said cylinder head partition having a cylindrical bore smaller in diameter than either of said working enginecylinders, a reciprocable element passing through said bore in the cylinder head partition and fastened to each of said pistons so as to reciprocate with the pistons, each of said working engine cylinders havin within it a power chamber, said power chambers being adjacent said cylinder head partition, at least two spark plugs fastened into said structural cylinder at locations which place the plugs points of ignition in communication with their respective said power chambers, said inserted cylinder head partition having at least two annular grooves in its outer cylindrical surface, asealing ring of pliable material such as an elastomer in each of said annular grooves, said inserted cylinder head partition having within it a chamber for the circulation of liquid coolant, said structural cylinder having openings in its wall for the entrance and exit of the liquid coolant into and out of said coolant chamber, said openings in the wall of the structural cylinder for the passage of coolant being located between said sealing rings of pliable material so as to prevent leakage of liquid coolant into said power chambers, said sealing rings of pliable material also serving to prevent leakage of high'pressure combustion gases from each power chamber into the other power chamber and into the cooling passages, said retaining means in the wall'of the structural cylinder being removable so as to permit removal of said inserted cylinder head partition from the bore of the structural cylinder, and said annular coolant chamber serving to prevent, saidpliable seal rings from being damaged by the heat of combustion in said power chambers.

12. In a double acting two stroke cycle internal combustion engine, the combination of a crankcase, a crankshaft rotatably mounted in said crankcase, a front cylinder connected to said crankcase, a front piston reciprocable in said front cylinder, a connecting rod for con- :verting the reciprocating motion of saidfront piston to the rotary motion of said crankshaft, a back cylinder mounted behind said front cylinder, a back piston reciprocable in said back cylinder, a cylinder head located between said cylinders, said cylinder head having a cylindrical bore smaller in diameter than either of said cylinders, said two pistons being mechanically interconnected through said bore in the cylinder head so as .to. reciprocate in unison, each of said pistons having a reduced diameter tubular section extending into said bore in the cylinder head and reciprocable therein, eachofsaid tubular seetions havingat least one ring groove and a seal ring in the groove adapted to sealwithin said cylindrical bore in Q the cylinder head, said cylinder head having inlet ports 1 interrupting its cylindrical bore near each end, said inlet ports being controlledbyjtheir respective said tubular sections, said front cylinder and 'saidlback cylinder ea'ch having" exhaust ports controlled by their respective piston,

said front cylinder and said back cylinder each having a power chamber adjacent said-cylinder head, means for supplying scavenge air'to the interior of at least one of said tubular sections, and each 'of said power chambers having aunifiow type scavenging operation with inlet through said inlet ports andexhausting through said exhaust ports. I c a 1 The combination recitedinclaim 12 wherein said reduced diameter tubular section and then radially outward through said gap into said inlet ports.

15. In a double acting two-stroke cycle internal combustion engine, the combination of two cylinders mounted in tandem, a working piston reciprocable in each of said cylinders, a cylinder head located between said cylinders, said cylinder head having a bore smaller in diameter than either of said cylinders, said two working pistons being mechanically interconnected through said bore in the cylinder head so as to reciprocate in unison, a reduced diameter valve piston attached to each of said working pistons, said valve pistons extending into said bore in the cylinder head and reciprocable therein, each of said valve pistons having at least one circumferential ring groove and an expanding type seal ring in the groove for sealing within said bore in the cylinder head, said cylinder head having inlet ports interrupting its cylindrical bore near each end, said inlet ports being controlled by their respective valve pistons, each of said cylinders having exhaust ports controlled by their respective working piston, said cylinders each having a power chamber adjacent said cylinder head, means for supplying scavenge air to the interior of at least one of said valve pistons, and each of said power chambers having a uniflow type scavenging operation with inlet through said inlet ports and exhausting through said exhaust ports.

16. In a double acting two stroke cycle internal combustion engine, the combination of a crankcase, a crankshaft rotatably mounted in said crankcase, a front cylinder connected to said crankcase, a front working piston reciprocable in said front cylinder, a connecting rod for converting the reciprocating motion of said front working piston to the rotary motion of said crankshaft, a back cylinder mounted behind said front cylinder, a back working piston reciprocable in said back cylinder, a cylinder head located between said cylinders, said cylinder head having a cylindrical bore smaller in diameter than either of said cylinders, said two working pistons being mechanically interconnected through said bore in the cylinder head so as to reciprocate in unison, each of said working pistons having a reduced diameter valve piston extending into said bore in the cylinder head and reciprocable therein, each of said valve pistons having at least one ring groove and an expanding type seal ring in the groove adapted to seal within said cylindrical bore in the cylinder head, said cylinder head having a first set of ports interrupting its cylindrical bore near one end and a second set of ports interrupting its cylindrical bore near the other end, said first set of ports being controlled by one of said valve pistons, said second set of ports being controlled by the other said valve piston, said front cylinder having a third set of ports controlled by the front working piston, said back cylinder having a fourth set of ports controlled by the back working piston, said front cylinder and said back cylinder each having a power chamber adjacent said cylinder head, means for supplying scavenge air to the two power chambers through two sets of said ports, and both of said power chambers having a unifiow type scavenging operation with inlet through two sets of said ports and exhaust through two sets of said ports.

17. In a double acting two stroke cycle internal combustion engine, the combination of a crankcase, a crankshaft rotatably mounted in said crankcase, a structural cylinder mounted to said crankcase, a cylinder head partition inserted into said structural cylinder so as to divide the structural cylinder into two individual working cylinders, retaining means for retaining said cylinder head partition in axial location within said structural cylinder, :1 reciprocable piston in each of said working cylinders, said cylinder head partition having a bore smaller in diameter than either of said working cylinders, a reciprocable member passing through said bore in the cylinder head and fastened to both of said pistons so as to reciprocate in unison with the pistons, a connecting rod for converting the reciprocating motion of said pistons to the rotary motion of said crankshaft, each of said working cylinders having a combustion chamber adjacent said cylinder head partition, said inserted cylinder head partition having a passage around the bore in the cylinder head for the flow of liquid coolant, said structural cylinder having passages through its wall for the entrance and exit of the liquid coolant into said cooling passage in the inserted cylinder head, and sealing means for preventing the leakage of the liquid coolant into each combustion chamber and for preventing the leakage of combustion gases out of each combustion chamber into the cooling passages.

18. In a double acting two stroke cycle internal combustion engine, the combination of a crankcase, a crankshaft recipr'ocable in said crankcase, a front and a back cylinder coaxially mounted to said crankcase, front and back pistons reciprocable in their respective cylinders, a cylinder head located between said cylinders, said cylin der head having a bore smaller in diameter than either of said cylinders, each piston having a reduced diameter tubular section extending into the bore in the cylinder head and reciprocable therein, a reciprocable rod attached to said front piston and passing through said tubular sections, a perforated cone structure with its base attached to said back piston and its apex attached to said reciprocable rod, said cone structure being mounted in the direction with the base of the cone nearer said crankshaft than the apex, means for supplying scavenge air to the interior of said back cylinder, the perforations in said cone being for the passage of said scavenge air, each of said cylinders having exhaust ports in its wall controlled by its respective piston, and each of said cylinders having a uniflow type scavenging operation exhausting through said exhaust ports.

References Cited in the file of this patent UNITED STATES PATENTS 758,854 Russell May 3, 1904 827,759 Smith Aug. 7, 1906 874,634 St. Germain Dec. 24, 1907 896,870 Taylor Aug. 25, 1908 1,149,521 Hunter Aug. 10, 1915 1,259,391 Gildersleeve Mar. 12, 1918 1,354,571 Leblanc Oct. 5, 1920 1,440,825 Guaita Jan. 2, 1923 1,900,133 Schaelfers Mar. 7, 1933 1,955,620 Buchi Apr. 17, 1934 2,615,428 Deardorff et a1. Oct. 28, 1952 FOREIGN PATENTS 469,532 Germany Dec. 13, 1928 

1. IN A DOUBLE ACTING TWO STROKE CYCLE INTERNAL COMBUSTION ENGINE, THE COMBINATION OF A CRANKCASE, A CRANKSHAFT ROTATABLY MOUNTED IN SAID CRANKCASE, A FRONT CYLINDER MOUNTED ON SAID CRANKCASE, A FRONT PISTON RECIPROCABLE IN SAID FRONT CYLINDER, A CONNECTING ROD FOR CONVERTING THE RECIPROCATING MOTION OF SAID FRONT PISTON TO THE ROTARY MOTION OF SAID CRANKSHAFT, A BACK CYLINDER MOUNTED BEHIND SAID FRONT CYLINDER, A BACK PISTON RECIPROCABLE IN SAID BACK CYLINDER, A CYLINDER HEAD LOCATED BETWEEN SAID FRONT CYLINDER AND SAID BACK CYLINDER, SAID CYLINDER HEAD HAVING A CYLINDRICAL BORE SMALLER IN DIAMETER THAN EITHER OF SAID CYLINDERS, A RECIPROCABLE ROD PASSING THROUGH SAID BORE IN THE CYLINDER HEAD, SAID RECIPROCABLE ROD BEING FASTENED TO EACH OF SAID PISTONS SO AS TO RECIPROCATE WITH THE PISTONS, BOTH OF SAID PISTONS HAVING A TUBULAR SECTION EXTENDING INTO SAID CYLINDRICAL BORE IN THE CYLINDER HEAD AND ADAPTED TO RECIPROCATE THEREIN, EACH TUBULAR SECTION BEING FITTED WITH AT LEAST ONE EXPANDING TYPE SEAL RING, SAID TUBULAR SECTIONS ENDING WITHIN SAID CYLINDRICAL BORE, SAID TUBULAR SECTIONS SERVING TO CONDUCT AIR, SAID RECIPROCABLE ROD SERVING TO TRANSMIT THE FORCE OF COMBUSTION FROM SAID BACK PISTON TO SAID CONNECTING ROD, A DISK ATTACHED TO SAID RECIPROCABLE ROD AND LOCATED BETWEEN THE ENDS OF SAID TUBULAR SECTIONS, SAID DISK CONFORMING AT ITS OUTER DIAMETER TO SAID CYLINDRICAL BORE IN THE CYLINDER HEAD SO AS TO FORM A SLIDING SEAL, AND THE PURPOSE OF SAID DISK BEING TO PREVENT LOSS OF AIR PRESSURE FROM THEINTERIOR OF EACH TUBULAR SECTION INTO THE OTHER AS EACH PISTON ALTERNATELY PUMPS AIR FOR SCAVENGING. 